The present invention relates to monitoring of airbag deployment with a tape, and methods and circuits for processing a stream of data received from a sensor that monitors the rate at which the tape is being withdrawn from a cartridge.
Experience has shown that airbags work best in combination with seat belts and other safety systems. Although airbags contribute to the overall safety of occupants of an automobile, they can present a danger to a vehicle occupant who is positioned too close to an airbag when it deploys. This condition, where the vehicle occupant is positioned so that airbag deployment might be dangerous, is referred to as the vehicle occupant being xe2x80x9cout of position.xe2x80x9d Various systems have been developed to detect an xe2x80x9cout of positionxe2x80x9d vehicle occupant. Sensor systems designed to detect the vehicle occupant""s position often require constant monitoring so that in the event of a crash the vehicle occupant""s position is known. Sensor systems designed to detect the position of the vehicle occupant have been proposed based on ultrasound, optical, or capacitance sensors.
Constant monitoring of sensors, which may have high data rates, requires the design of algorithms which can reduce sensor data to a single condition or a limited number of data conditions which are used in an airbag deployment decision to prevent airbag deployment or for a duel stage airbag to select the level of deployment. Maintaining data integrity between the non-crash positional data, and positional data needed during airbag deployment is complicated by the noisy environment produced by a crash. Dealing with data integrity issues requires increased processor capabilities and algorithm development, which also requires additional testing.
Prior art approaches attempt to determine, based on various sensors, the distance between the airbag and the passenger before the airbag is deployed. In many instances, the vehicle occupant will not be too close to the airbag at the time the decision to deploy the airbag is made, but, because of the rate at which the vehicle occupant is approaching the airbag, the vehicle occupant will be too close when the airbag is actually deploying. To handle these situations, more sophisticated sensors and algorithms are needed in order to attempt to predict the vehicle occupant""s position when the airbag is actually deployed or nearly completely deployed. In other words, the ideal airbag deployment system functions such that the airbag deploys fully or nearly fully before the vehicle occupant engages the airbag. Existing systems inhibit airbag deployment when, based on various sensors and algorithms, it is determined that, because of the position of the vehicle occupant, the bag is more likely to harm than to benefit the vehicle occupant.
Successfully creating a sensor and algorithm system is complicated because there is usually very little delay between the decision to deploy and actual deployment. This is so because the maximum benefit from an airbag is achieved by early deployment, and at the same time, more time before deployment maximizes the information available to determine whether deployment is necessary. The desire to maximize effective deployment of the airbag while minimizing unnecessary deployment creates a tension between waiting for more information and deploying immediately. Therefore, once sufficient information is available, deployment typically follows nearly immediately.
A system which employs vehicle occupant position sensors and algorithms must be able to supply at all times an indication of whether airbag deployment should be inhibited so that the inhibit decision can be applied whenever the airbag deployment decision occurs. This means the sensors and algorithms used to develop the vehicle occupant position inhibit signal, cannot be optimized to deal with a specific time frame in which the actual deployment decision is made. The end result is that such algorithms may be less accurate than desired because they must predict events relatively far in the futurexe2x80x94perhaps tens of milliseconds.
One known type of sensor shown in EP 0990567A1, employs a plurality of tapes which extend between the front of the airbag and a tape dispensing cartridge mounted on the airbag housing. Tape extraction sensors within the cartridge monitor the rate at which tape is withdrawn from the cartridge and thus can detect airbag impact with a vehicle occupant by a decrease in airbag velocity. This type of sensor which can monitor the way an airbag is actually deploying solves the problem of predicting whether a vehicle occupant will be out of position at time of airbag deployment. In this arrangement the airbag is deployed, and if it encounters a vehicle occupant before it has reached a certain stage of deployment the airbag is vented which effectively removes the airbag. Several tapes and tape dispensing cartridges are used to monitor different portions of the bag so that if any portion of the bag contacts a vehicle occupant, the fact of contact can be detected and the bag vented to prevent injury to the out-of-position occupant. To be practical, this type of sensorxe2x80x94which monitors actual deploymentxe2x80x94needs simple but robust techniques for monitoring the rate at which tape is withdrawn from the cartridge.
The airbag deployment sensor of this invention has a cartridge in which a quantity of tape is stored. One end of the tape is attached to the inside surface of an airbag cushion so that when the cushion is deployed it pulls tape from the cartridge. The rate at which the tape is pulled from the cartridge is monitored by transmitting light through the tape, or by detecting the presence of the metalized or ferrous portions of the tape.
In a first embodiment a tape xc2xd mm by 5 mm constructed of black polyethylene has 2 mm diameter holes spaced 5 mm on center extending along the length of the tape. An infrared light emitting diode is positioned on one side of the tape and a phototransistor is positioned opposite the light emitting diode. The phototransistor is connected to a comparator circuit with hysteresis that provides a clean digital output proportional to the rate at which the holes formed in the tape are pulled past the phototransistor. Alternatively, an infrared transparent tape on which an infrared opaque pattern has been printed may be used.
In a second embodiment, a tape xc2xd mm by 5 mm has 5 mm regions that are spaced 5 mm apart, which have been metalized. For example, a metal film may be deposited on Mylar(copyright) tape and selectively etched to form metalized regions or metalized paint may be used on film or cloth. The metalized regions may be detected by one of three methods. The first method employs two closely spaced contacts that are connected by the metalized regions as they pass over the contacts. This type of detector may also be connected to a comparator circuit with hysteresis to provide a digital outlet. The second method for detecting the passage of the metalized regions employs a capacitive plate as a sensor. The capacitive plate is part of an oscillator circuit where the frequency of the oscillator circuit is controlled by the capacitance of the capacitive plate. As the metalized regions move opposite the capacitor plate, a variable capacitor is formed so that the amount of capacitance in the circuit changes. With this varying capacitance, the frequency of the oscillator increases and decreases as the metalized regions pass the capacitor plate. A third method of detecting the rate at which a tape with metalized regions is pulled from the cartridge employs an amplitude modulated signal. An oscillator of a few hundred kHz to about 1 MHz is connected into a first electrode. A second electrode spaced from the first electrode is connected to an amplification circuit. The metalized region forms a capacitive link between the first electrode and the second electrode that efficiently transmits the oscillator signal to the amplifier. Therefore as the metalized regions pass the first and second electrodes, the signal received by the amplifier circuit varies in amplitude. The output of the amplifier is rectified, producing a pulsed DC output.
If the metalized region is formed from a ferromagnetic alloy, movement of the ferromagnetic region can be used with a permanent magnet to affect a magnetic field sensor such as a Hall effect sensor, a GMR sensor, or even a simple conductor loop or coil. The permanent magnet is positioned opposite the magnetic field sensor, and the ferromagnetic metalized region acts as a magnetic shield selectively blocking magnetic field lines from the permanent magnet to the magnetic field sensor.
It is a feature of the present invention to provide a tape that is drawn from a cartridge to detect airbag cushion employment rate that is constructed to reliably affect a sensor.
It is a further feature of the present invention to provide methods for detecting the velocity of a tape being pulled from a cartridge by an airbag cushion.
It is another feature of the present invention to provide a tape sensor combination that employs detecting a change in capacitance.
It is a still further feature of the present invention to provide a tape, sensor combination that employs detecting a change in magnetic field strength.
It is another feature of the present invention to remind a tape sensor arrangement that can accommodate variations in sensor performance due to device to device variation and aging effects.
Further features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.